my firstborn, my might, and the beginning of my strength
The phrases "my firstborn, my might" and "the beginning of my strength" mean the same thing. The words "might" and "strength" stand for Jacob's ability to produce children. The words "firstborn" and "beginning" mean that Reuben is his first child. AT: "my first child after I became a man" (See: rc://en/ta/man/translate/figs-parallelism)
outstanding in dignity, and outstanding in power
This can be stated as a new sentence. AT: "You are first in honor and power" or "You surpass everyone else in honor and power"
Uncontrollable as rushing water
Jacob compares Reuben to water in a strong current to emphasize that he cannot control his anger and he is not stable. (See: rc://en/ta/man/translate/figs-simile)
you will not have the preeminence
"you shall not be first among your brothers"
because you went up to your father's bed. Then you defiled it; you went up to my couch
Here "bed" and "couch" stand for Jacob's concubine, Bilhah. Jacob is referring to when Reuben slept with Bilhah (See: Genesis 35:22). AT: "because you went to my bed and slept with Bilhah my concubine. You have shamed me" (See: rc://en/ta/man/translate/figs-metonymy)
you went up to your father's bed ... you went up to my couch
Both statements mean the same thing. (See: rc://en/ta/man/translate/figs-parallelism)